This invention relates to an image recording apparatus for recording an image onto a photo-sensitive recording medium in accordance with given image information.
An image recording apparatus of the kind referred to above is conventionally known, in which a light is applied to an original, and the light reflected by or transmitted through the original is caused to pass through an optical system including a reflecting mirror, an optical filter, lenses and the like. A photo-sensitive recording medium is exposed to the light by the optical system, so that a latent image corresponding to an image on the original is formed on the photo-sensitive recording medium.
In the above image recording apparatus, when the image on the original is of a so-called continuous tone in which the lights and darks of the image varies continuously like photographs or pictures, the photo-sensitive recording medium high in gamma value is employed in which a color-development concentration changes abruptly with respect to a light exposure so that a contrasty image can be recorded on the photo-sensitive recording medium. In this case, a halftone screen having a dot pattern is arranged on an optical path extending between the original and the photo-sensitive recording medium, to expose the recording medium to the light having passed through the halftone screen. Such arrangement is advantageous in that the gradation reproducibility of the photo-sensitive recording medium can be improved. Specifically, when the halftone screen of, for example, a cross-stripe pattern is employed, the exposure of the light transmitted through one of transparent portions of the halftone screen and arriving at the photo-sensitive recording medium varies depending upon the darks and lights of the image on the original as indicated respectively by (a) and (b) in FIG. 13. As the exposure of the light arriving at the photo-sensitive recording medium exceeds a critical level, a portion on the recording medium, at which the light arrives, is developed with a constant concentration so that the darks and lights of the image on the original are replaced respectively by a large spot and a small spot as indicated respectively by (c) and (d) in FIG. 13. In this manner, the difference between the darks and lights of the image on the original is expressed as an area gradation by the size and distribution density of dots. Thus, it is possible to improve the gradation reproducibility of the photo-sensitive recording medium.
According to the conventional apparatus described above, if the halftone screen is employed when the image on the original is of a continuous tone, the gradation of the image recorded on the photo-sensitive recording medium is improved. However, if the halftone screen is employed for the original in which the lights and darks of the image on the original are expressed by dots different in size from each other, interference between the dots of the image on the original and the halftone screen causes interference fringes or moire to be formed on the image recorded onto the photo-sensitive recording medium. This raises such a problem that the image recorded onto the recording medium becomes blurred.